Fig. 4.  Activated p38 mitogen-activated protein kinase (MAPK) mediates nerve growth factor (NGF)–dependent increases in immunoreactive μ-opioid receptor (MOR) (red fluorescence ) of calcitonin gene–related peptide (CGRP) positive (green fluorescence ) sciatic nerve neurons. After intraplantar Freund's complete adjuvant (FCA), anterogradely transported MOR immunoreactivity (A, D, G ) in immunoreactive CGRP neurons (B, E, H ) was assessed at the site of a sciatic nerve ligature after intraplantar vehicle (A –C ), intraplantar NGF (D –F ), and intraplantar NGF plus intrathecal p38-MAPK inhibitor SB203580 (G –I ). (C, F, I ) Combined confocal immunofluorescent images show the increased accumulation of MOR immunoreactivity proximal to the ligature of the sciatic nerve ipsilateral to the NGF-injected hind paw (D –F ) compared with that of vehicle (A –C ). This increase was abolished after treatment with intraplantar p38-MAPK inhibitor SB203580 (G –I ). Bar = 20 μm.